Dynamical Nonplanarity of Benzene. Evidences from the Car-Parrinello Molecular Dynamics Study

Car-Parrinello molecular dynamics simulation of an isolated benzene molecule unextectedly revealed very low population of a planar geometry of the ring (less than 10%) despite the ideal aromatic character of a cyclic conjugated system. Analysis of nonplanar conformations of benzene in terms of puckering parameters demonstrates that benzene in the gas phase exists mainly as a mixture of two mirror-symmetrical families of flattened boat and twist boat conformations with a total population of more than 70%. The average conformation of the ring is nonplanar with values of endocyclic torsion angles of 6.7 degrees.